Download Clever Dumb Antenna: Passive Multibeam Antenna

Clever Dumb Antenna: Passive Multibeam Antenna for
Broadband Wireless Communication
Dr. John Howard and Chuck Fung
Electromagnetic Technologies Industries, Inc., 50 Intervale Rd, Boonton, NJ 07005 USA
www.etiworld.com
Abstract — A passive multi-beam antenna systems with
beamforming technology that can be used to increase quality
of service, network capacity, and spectrum to meet the
current and future demand of data usage and network
capacity is presented. The system presented can produce as
many as 32 narrow high-gain beams in a 120° sector with
beam crossing set to be between 3 to 10 dB. Each beam
provides a capacity and throughput multiplication over a
traditional cell site. Frequencies can be reused in a sector
resulting in a spectrum multiplication of as many as 32
times. With the use of multiplexers several channels can be
combined and transmitted in each beam providing multiband/ multi-channel transmission with a single antenna
system to further increase user capacity and throughput.
Index Terms — Beamforming Networks, Frequency Reuse,
systems can divide up a 360° cell site into several narrow
high-gain sectors. Fig. 1 shows a typical cell site with
three 120° sector antennas and multi-beam antenna
systems (MAS) producing more sectors.
Multifrequency Antennas, Phased Arrays, Spectrum Multiplier
Antenna
I. INTRODUCTION
Multi-beam antennas can provide increased wireless
capacity with enhanced spectral efficiency. A method to
enhance spectral efficiency is to use space division
multiple access (SDMA) techniques. SDMA methods
provide higher user capacity in a limited frequency
spectrum. SDMA techniques are implemented by most
wireless providers to optimize the use of available
spectrum [1]. Typically, wireless providers use three
sectors in a 360° coverage area. With the passive multibeam antenna system spectrum and capacity can be
multiplied as many as 32 times within 360° coverage,
providing 96 dual polarized beams. The benefit of such a
system is higher data throughput, higher customer
capacity, increased spectral efficiency, and reduced
number of cell sites versus traditional coverage [2]. With
the use of multiplexers, several frequency channels can be
merged and transmitted into a single beam producing a
multi-channel sector.
For every channel that is
transmitted into the beam, an increase in capacity and
throughput factor is obtained.
II. MULTI-BEAM ANTENNA SYSTEM
Multi-beam antenna systems are the solution to the ever
growing demand of data usage and network capacity in
urban environments. Multi-beam phase array antenna
1
Fig. 1: Traditional versus Multi-beam Comparison
Each beam is accurately spatially aligned by a
beamforming network while a beam-shaping network
shapes the radiation envelope of each lobe. The beam
former network focuses each beam in a specific direction
electrically and the beam-shaping network minimizes the
possibility of interference radiating from the antenna in a
sector. Because the beams are narrow and are focused in
a specific direction, the individual beams are spatially
isolated. Although the gains of these antennas are higher
than the traditional antennas currently being deployed
(15-16dBi), the systems presented herein can achieve the
same footprint if required by tilting the antenna.
Otherwise, the gain can be employed to reduce the
number of site in an area. The gain of such a multi-beam
antenna is 18- 27dB.
This type of beamforming networks can be designed to be
broadband and can provide multi-band coverage allowing
for multi-band and multi-channel coverage (4). More
complex butler matrix BFN such as the 8x8 or the 16x16
butler matrix can be designed to produce additional beams
but the design realization becomes very difficult with
increasing numbers of passive microwave components
and cross overs needed to obtain the correct phases [5].
An equation used to obtain the phase per a given mode of
the butler matrix is:
As the number of narrow non-overlapping
beams/sectors in a cell site increases so does the capacity
and throughput. Although Fig. 1 illustrates several
different frequencies being reused, UMTS where
frequencies reused in a single site and also adjacent sites
are a standard method of communication can also be used
to increase capacity and quality of service. With the use
of multiplexers with this system, multi-channel sectors in
one or multiple bands can be created allowing for multicarrier and multi-channel support.
The antenna system being presented is named as the
“Clever Dumb Antenna” because it contains all passive
components. A growing trend in communication industry
is the use of tunable smart antennas. These antenna
systems are commonly paired with variable microwave
components such as phase shifters controlled by
microprocessors which can be used to move the position
of the beam in both azimuth and elevation to target
densely populated areas. However, tunable components
require additional power sources and are not as reliable.
The clever dumb antenna system provides complete 360°
coverage at all times. Being a passive system, it is robust
and does not require a power source and maintenance.
(1)
k = mode of matrix
N = total number of output modes
n = output port number
Ψ= Phase output in Radians
Using the equation above, the phase of each output can be
calculated for each mode with any number of outputs.
The phases of each output for each mode can be seen in
the table below in Fig. 3.
M1
M3
M2
M4
III. BEAMFORMING NETOWRK (BFN)
A1
0°
0°
0°
0°
A2
45°
-135°
135°
-45°
A3
90°
90
-90°
-90
A4
135°
-45°
45°
135°
Fig. 3: 4 x 4 Butler Matrix Phase Chart
A beamforming network (BFN) is a network comprised
of several passive microwave components. As the number
of beams increase so does the complexity of the BFN.
The BFN provides the required phases and amplitudes of
signal between the antenna and system transceivers. A
BFN shapes the beams from the antenna array and steers
their directions electronically without need for mechanical
motion. Such a system can be designed with time or
frequency domain analysis of the electrical and
microwave components. An example of a simple BFN is
a 4 by 4 butler matrix that can be produced with four 90°
hybrids and two 45° phase shifters connected in the block
diagram shown in Fig. 2 where the M1 through M4
represents the input of the signal and A1 to A4 are the
connections to the antenna [3].
IV. Passive Multi-beam Antenna System
The passive multi-beam antenna system consists of
several antenna array columns adjacent to each other.
The picture on the left seen in Fig. 4 below shows the
beamforming network connected to one of ETI’s antenna
while the picture on the right is another type of antenna
design that allows for reconfiguration.
Fig. 4: ETI Multi-beam Antenna Systems
Phase matched cables are used to connect from the
beamforming network to the antenna system to maintain
the correct steering position of the multi-beam system.
The passive multi-beam antenna system employs complex
passive beamforming techniques to allow for frequency
reuse. Interference between each beam is reduced using a
propriety technique. In addition, beam-shaping methods
Fig. 2: 4 x 4 Butler Matrix BFN
2
Communications and Signal Processing, Proceedings of the
1998 South African Symposium on Communication and
Signal Processing, pp. 161- 164, Sept. 7-8, 1998.
[2] J. Howard and J. Desai, “Multibeam Antenna Serves
Broadband Wireless Coms”, Microwaves & RF, Vol. 47
Issue 6, pp. 61, June 2008.
[3] C. Collado, G. Alfred, and F. De Flaviis, “Dual-band butler
matrix for WLAN systems,” Microwave Symposium
Digest in IEEE MTT-S Int. Microwave Symposium Digest,
June 12-17 2005, pp. 2247–2250
[4] J. Howard. J. Logothetis and J. Wilson, “Beamformer:
Broadband RF Technology For Integrated Networks”,
Antennas and Propagation Society International Symposium,
1996. AP-S. Digest , vol.3, pp.1632,1635, July 21-26 1996
[5] M.E. Bialkowski, F.E. Tsai and Y. Su, K. Cheng, “Design of
fully integrated 4x4 and 8x8 Butler matrices in
microstrip/slot technology for ultra wideband smart
antennas," Antennas and Propagation Society International
Symposium, 2008. AP-S 2008. IEEE , July 11 2008
[6] M.S Smith and T.G. Tan, "Sidelobe reduction using random
methods for antenna arrays," Electronics Letters , vol.19,
no.22, pp. 931-933, October 27 1983
[7] A. H. Aboud and K. H. Sayidmarie, "Reduction of sidelobe
in phased arrays", International Conference on Radio
Science, Asia-pacific, pp. 70-73, August 2004.
are deployed to reduce side lobe levels to minimize
interference between beams [6]-[7]. An example of a
multi-beam antenna system radiation pattern can be seen
in Fig. 5 below.
Fig. 5: Radiation Pattern of a 4 Beam Antenna System
The multi-beam system being shown produces 4 beams
in a 120° sector. The system produces side lobe levels
25dB below the maximum gain of the main beam.
Because of this, all 4 beams can transmit at the same time
effectively, with minimal interference. The number of
beams for a given sector of 90° or 120° can be modified
with a change in the beamforming network while using
the same antenna. This gives the user an option of
upgrading a similar system with fewer to a more
advanced system with a larger number of beams to meet
user and data demand growth.
An example of
performance specification a beamforming network is
shown in Fig. 5.
Dr. John Howard founded Electromagnetic
Technologies Industries, Inc. (ETI) in 1996
after a 20-year career at some of the world’s
leading technology companies. He has held
senior engineering positions at companies the
likes of Merrimac Industries, Narda (Loral)
Microwave Corporation, RCA Astro Lab - Satellite Systems Division,
Marconi Space and Defence Systems - Corporation Radar and Missile
Systems Division and the British Aerospace Corporation. During his
extensive career, Dr. Howard has managed to make time to share his
knowledge and experience as an Assistant Professor at Chelsea College,
University of London, UK from 1976 thru 1978 and then as an Adjunct
Professor at Polytechnic of New York in Farmingdale, NY from 1983
thru 1984 and finally as an Adjunct Professor at New Jersey Institute of
Technology from 1989 thru 1993.Dr. Howard’s work has earned him
several awards including the Marconi Space and Defence Systems
Award in 1980 for his work in Innovative Electronic Countermeasures
Solution and the RCA Award for Authors & Inventors in 1983.Dr.
Howard boasts over 85 published papers on Antennas, Beamformers,
Defense and Telecommunications Systems, Filters, Microwaves and
Electromagnetic Theory. While attending University College Cardiff,
University of Wales University College London, University of London
and Chelsea College, University of London he earned degrees in
Electrical and Electronic Engineering, Microwave Engineering,
Microwaves and Modern Optics and most notably a Ph.D. in Satellite
and Terrestrial Communications.
V. CONCLUSION
A traditional 360° cells sites is divided up into three
sectors. With the passive multi-beam antenna systems,
spectrum and capacity can be multiplied as many as 32
times within 360° coverage, providing 96 dual polarized
beams. The benefit of such a system is higher data
throughput, higher customer capacity and increased
spectral efficiency. The beam crossing can be designed to
cross between 3 to 10 dB with side lobe levels of 25dB,
allowing the system to be used for GSM and UMTS. As
the number of beams increases, so does the capacity and
throughput. With the use of multiplexers, multi-channel
sectors can be created to further enhance the benefits of
the system. The multi-beam antenna system is clearly
the solution to the ever growing demand of data usage and
network capacity for the finite amount of spectrum.
Chuck W. Fung is the Vice President of
Technology at Electromagnetic Technologies
Industries, Inc. (ETI).
Chuck has worked for ETI since 2011 with a
focus on antenna design and beamforming
networks for RF systems. He holds a BS in Electrical and Computer
Engineering at Worcester Polytechnic Institute. Mr. Fung’s experience
includes the design and manufacture of low profile, directional, high
gain antennas for Wi-Fi applications. His computer work involves the
design, programming, construction, and testing of robots.
REFERENCES
[1]
M.P. Lotter and P.Van Rooyen, “An Overview of Space
Division Multiple Access Techniques In Cellular Systems”,
3